The program, covering the principal factors affecting man's physiological and behavioral response to his thermal environment and their implication for his health, consists of four projects: #1. Heat Transfer from the Skin Surface to the Environment in Man: The processes of heat exchange by radiation, convection, conduction and evaporation are examined in terms of temperature and vapor pressure gradients and the associated heat and mass transfer coefficients, which in turn are dependent on clothing insulation, air motion and barometric pressure. Rational temperature indices of heat stress and of physiological heat strain caused by the total environment (including water immersion) are being developed. #2. Interactions Between Physiological Systems Regulating Circulation, Respiration and Body Temperature: The response and interaction of internal regulation by circulation, sweat secretion and respiration are related during rest and exercise to external thermal stresses of different origins. #3. Thermal Psychophysics and Human Behavioral Thermoregulation: Sensations of cold, warmth, pleasure and discomfort are quantitatively related to internal regulatory changes, to behavioral changes and to temperature indices of the thermal environment. #4. Theoretical Models of the Physiological and Behavioral Temperature Regulation and the Thermal Environment: Mathematical models are developed for interpreting observations, testing concepts and predicting man's response to complex thermal environments.